1. Field of the Invention
The present invention relates to a semiconductor device comprising a plurality of semiconductor chips stacked in the direction of thickness, and a method for making the same.
2. Background Art
There is known a type of semiconductor device in which a plurality of semiconductor chips are stacked and sealed in a resin package for drastically increased circuit mounting density. Such a semiconductor device is called xe2x80x9cchip-on-chipxe2x80x9d type because of the stacking arrangement in which one of the chips is mounted on another.
FIG. 29 shows an arrangement of a prior art chip-on-chip semiconductor device. As understood from the figure, in this arrangement, a plurality of semiconductor chips 9a-9c are stacked successively on a surface of a substrate 90. According to such an arrangement, an area occupied by the semiconductor chips 9a-9c on the surface of substrate 90 is small, advantageously increasing the mounting density of the semiconductor devices.
However, the prior art has following problems.
Specifically, when the plurality of semiconductor devices 9a-9c are stacked, respective electrodes 94a-94c are elevated accordingly to higher locations. As a result, the electrodes 94c of the highest semiconductor 9c are located disadvantageously high (height difference Ha), away from the surface of substrate 90 formed with terminals 92 to which the electrodes 94a-94c are to be connected via respective pieces of wire 93.
Under such a situation, it is sometimes difficult to make a proper connection between the electrode 94c and the terminal 92 because of the big height difference Ha. Specifically, in a conventional wirebonding machine, a capillary can perform a proper bonding only within a vertical range of xc2x1300 xcexcm away from its baseline height. Sometimes, however, the height difference Ha is greater than the upper limit (i.e. greater than the baseline height added with +300 xcexcm), making it impossible to use the wirebonding machine for the wirebonding operation. In addition, when the height difference Ha is large, as shown in FIG. 30, the capillary 95 has to be significantly tilted when the capillary 95 presses the wire 93 to the electrode 94c or the terminal 92. Under such a circumstance, there develops a space S between a tip portion of the capillary 95 and the electrode or the terminal, making it impossible to properly bond the wire 93. As a result, according to the prior art, it is difficult to properly bond an end of the wire 93 to the electrodes 94a-94c or the terminal 92, and there is a significant risk of causing a faulty connection at the location where the wire is bonded.
It is therefore an object of the present invention to provide a semiconductor device of a chip-on-chip type which allows proper connection via wire between the electrodes in each of the semiconductor chips and respective terminals.
Another object of the present invention is to provide a semiconductor device of a chip-on-chip type which allows more appropriate connection between the electrodes in each of the semiconductor chips and corresponding terminals.
According to a first aspect of the present invention, there is provided a semiconductor device with a following arrangement. Specifically, the semiconductor device comprises a plurality of semiconductor chips stacked in the direction of thickness. Each of the semiconductor chips includes an upper surface formed with electrodes. The semiconductor device further comprises a plurality of terminal portions beside the semiconductor chips, and plural pieces of wire for electrical connection from the electrodes to respective terminal portions. Further, each of the terminal portions is at an elevation lower than the highest electrodes, and higher than the lowest electrodes.
According to the above arrangement, it becomes possible to decrease the height difference between each of the electrode on the semiconductor chips and corresponding one of the terminal portions to be connected via the wire, even if there is a large height difference between the uppermost electrodes and the lowermost electrodes in the stack of plural semiconductor chips. Therefore, it becomes possible to properly connect all of the electrodes on each of the semiconductor chips to respective terminal portions by means of wirebonding, within the vertical moving range of the capillary of the wirebonding machine. Further, it becomes possible to press the capillary of the wirebonding machine to each of the electrodes and terminal portions at a smaller angle of tilt so that the wire can be tightly pressed against the surface of the electrode or terminal portion.
According to a preferred embodiment, the wire is bonded to the electrode as the first bonding, and thereafter to the terminal portion as the second bonding.
Further, according to the preferred embodiment, the plurality of semiconductor chips are mounted on a die-pad portion of a lead frame. The lead frame has internal lead portions formed beside the die-pad portion for serving as the terminal portions, and the die-pad portion is lower in elevation than the internal lead portion by a predetermined distance.
According to another preferred embodiment of the semiconductor device, the semiconductor device includes a first semiconductor chip disposed at a lower elevation and a second semiconductor chip disposed at a higher elevation. The first semiconductor chip and the second semiconductor chip are stacked via a plate type supporting member, and the plate type supporting member is formed with the plurality of terminal portions, as well as openings for the wire to communicate between the terminal portions and the electrodes of the first semiconductor chip for electrical connection.
The supporting member may be a film type substrate made of a thin film of synthetic resin formed with a conductive wiring region, a lead frame made of a metal, or a plate type substrate having a surface formed with a conductive wiring region.
According to the preferred embodiment, the first semiconductor chip and the second semiconductor chip are stacked to sandwich the plate type supporting member.
According to another preferred embodiment, the second semiconductor chip is smaller than the first semiconductor chip, and the two semiconductor chips being directly stacked together. Further, the second semiconductor chip and the electrodes of the first semiconductor chip face the opening, and the upper surface of the first semiconductor chip has its circumferential region bonded to a lower surface of the plate type supporting member.
It should be noted here that the second semiconductor chip may be stacked by another or a plurality of semiconductor chips other than the second semiconductor chip or the first semiconductor chip.
According to a second aspect of the present invention, there is provided a semiconductor device having a following arrangement. Specifically, the semiconductor device comprises a plurality of semiconductor chips stacked in the direction of thickness, and a plate type supporting member for supporting the plurality of semiconductor chips. The plate type supporting member is formed with terminal portions for electrical connection with the semiconductor chips. The plate type supporting member is at an intermediate elevation between an uppermost surface and a lowermost surface of the stack of semiconductor chips. The supporting member is a film type substrate made of a thin film of synthetic resin formed with a conductive wiring region, a lead frame made of a metal, or a plate type substrate having a surface formed with a conductive wiring region.
According to the above arrangement, it becomes possible to keep the height difference between the electrodes on each of the semiconductor chips and the terminal portions on the plate type supporting member corresponding not greater than a predetermined distance. Thus, connection can be properly made between the electrodes and the terminal portions by means of wirebonding. In addition, it becomes possible to further reduce the overall thickness of the semiconductor device. It should be noted however, that the electrical connection between the terminal portions on the supporting member and the electrodes on the semiconductor chips may not necessarily be by means of wirebonding. Alternatively for example, one or both of the electrodes and the terminal portions may be formed with bumps for press-fit bonding.
According to a preferred embodiment, the first semiconductor chip is stacked with the second semiconductor chip. The first semiconductor chip has a main surface formed with the electrodes and facing upward. Further, the supporting member is formed with an opening penetrating the supporting member in the direction of thickness so that the electrodes of the first semiconductor chip are not covered by the supporting member. With is arrangement, the terminal portions on the supporting member and the electrodes on the first semiconductor chip can be adequately connected by wirebonding
According to another preferred embodiment, the supporting member is formed with a plurality of the above openings and a supporting region flanked by the openings. The first semiconductor chip and the second semiconductor chip are stacked to sandwich the supporting region. With this arrangement, the first and the second semiconductor chips can be advantageously supported by the plate type supporting member.
According to still another preferred embodiment, the second semiconductor chip is stacked so as not to cover the electrodes of the first semiconductor chip. Further, the second semiconductor chip has its main surface formed with the electrodes facing upward, and the electrodes of the first and second semiconductor chips are connected respectively to the terminal portions formed in the plate type supporting member via the wire.
According to still another preferred embodiment, the second semiconductor chip has the main surface facing downward, and is electrically connected to the first semiconductor chip. Further, one of the first semiconductor chip and the second semiconductor chip is electrically connected to the terminal portions formed in the plate type supporting member.
According to still another preferred embodiment, the terminal portions of the plate type supporting member extend into the opening. The electrodes of either the first semiconductor chip or the second semiconductor chip are connected to the extended terminal portions.
According to still another preferred embodiment, the first semiconductor chip and the second semiconductor chip are bonded to each other into the stack, and only one of the semiconductor chips is bonded to the supporting member.
According to still another preferred embodiment, the plate type supporting member is formed with an opening penetrating the supporting member in the direction of thickness. Further, the other of the first semiconductor chip and the second semiconductor chip is placed inside the opening while penetrating the opening vertically.
According to a third aspect of the present invention, there is provided a method for making a semiconductor device. The method for making this semiconductor device comprises a step of attaching a first semiconductor chip and a second semiconductor chip to a desired supporting member so that the first semiconductor chip is stacked by the second semiconductor chip. The supporting member includes an opening which penetrates the supporting member in the direction of thickness. The first semiconductor chip is fixed to a lower surface of the supporting member so that electrodes formed in the first semiconductor chip are faced to or exposed in the opening.
Other features and advantages of the present invention should become clearer from the detailed description to be made hereafter with reference to the attached drawings.